Circuit breaker



Oct. 25, 1949.

D. BOHN 2,486,104

CIRCUIT BREAKER Original Filed July 28, 1942 5 Sheets-Sheet l D. I. BOHN CIRCUIT BREAKER Oct. 25, 1949.

5 Sheets-Sheet 2 Original Filed July 28, 1942 W mm m m D JTTOPA/EY Oct. 25, 1949. D. l. BOHN 2,436,104

' CIRCUIT BREAKER Original Filed July 28, 1942 5 Sheets-Sheet 3 IN VEN TOR. 3i 2 W410 I BOHA D. l. BQH

CIRCUIT BRE 5 Sheets-Sheet 4 Original Filed July 28, 1942 Oct. 25, 1949. D. l. BOHN 2,486,104

CIRCUIT BREAKER Original Filed July 28, 1942 5 Sheets-Sheet 5 um i I INVENTOR.

Patented Oct. 25, 1949 CIRCUIT, BREAKER Donald 1. Bohn, Pittsburgh,

Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a

corporation of Pennsylv Original application July ania 28, 1942, Serial No.

452,613. Divided and this application March 1, 1944, Serial No. 524,540

8 Claims.

This application is a division of my Patent No. 2,412,247, issued December 10, 1946, and relates to circuit breaker apparatus and more particularly relates to a novel magnetic structure controlling the closing and trippin operation of a circuit breaker.

The circuit breaker of the present invention employs a magnet and armature design reducing the armature weight in a ratio of approxi mately 1:3, as contrasted with a conventional holding magnet. I

As will be obvious, in order to secure the same effective armature area for a smaller weight of armature, I may decrease the radius and correspondingly increase the length of the armature. Thus, an armature having a radius of 1%" and a length of 2.94" will weigh 1.582 pounds without mounting details. An armature whose radius is i and whose length is 6.45" will have the same effective armature area but weigh only .55 poundapproximate1y one-third the weight of the first armature.

Quite obviously, however, an armature of such great length compared to its diameter would be entirely impractical from a mechanical and stiffness point of View.

In accordance with my invention, I carry out this principle of weight reduction which over comes the mechanical defects noted above. In one form of my invention the armature weight is .55 pound and has an armature pull of 400 pounds.

I have discovered that I may materially reduce the mass of the armature and thereby increase the acceleration thereof by so arranging. the magnetic structure of the holding magnet that there are, in eiiect, a plurality of individual magnets, each with its individual armature.

Inasmuch as the center of the armature which is mechanically connected to the movable contact of the circuit breaker assumes the greatest share of the carrying load in operating the movable contact and this load on the armature is gradually reduced as the edges of the armature are approached, I provide maximum thickness of metal at the center of the armature with a tapering armature construction toward the ends to a substantially reduced thickness at the ends.

This serves to prevent any deflection of the center of the armature which might tend to occur if the armature were of uniform cross-section; such deflection at the center should it occur would result in a reduction of the holding force on the armature and hence result in a rapid pro,- grcssive release of the armature.

My novel circuit breaker provides for tripping of the breaker on de-energization of the holding" magnet armature and permits the armature of the magnet to be operated into engagement with the pole face of the magnet While the circuit breaker is still in disengaged position, the actual closing operations of the circuit breaker being performed by a separate power supply. This enables the use of a flexible connection from the armature to the movable circuit breaker contact, thus further reducing the mass and permitting a more rapid tripping operation.

Accordingly, an object of my invention is to provide a novel construction of a holding magnet in which tripping is eiiected by de-energization of the magnet armature.

Still a further' object of my invention is to provide a novel circuit breaker structure in which a flexible connection extends from the armature to the movable circuit breaker contact.

There are other objects of my invention which together with the foregoing will appear in the detailed description which is to follow, in connection with the drawings, in which:

Figure 1 is a schematic view of my circuit breaker operating element showing the contacts closed.

Figure la is a view of a commercial embodiment of the structure schematically shown in Figure 1.

Figure 2 illustrates the trip position of the circuit breaker in Figure 1.

Figure 2a is a view of a commercial embodiment of the structure schematically shown in Figure 2.

Figure 3 is a view corresponding to that of Figure 1 showing the movement of the apparatus for normally opening the circuit breaker.

Figure 4 is an exploded view in perspective of the operating magnet of my circuit breaker.

Figures 5, 6 and 7 are additional diagrammatic views further illustrating the operation of the magnet.

Referring now to Figuresl, 2 and 3, I have here shown in schematic form the construction and operation of a circuit breaker utilizing my invention. The circuit breaker here shown includes circuit connecting members II and I2, which form the terminals of the circuit breaker and are arranged to be connected into the external circuit.

An L-shaped stationary contact member I! having a contact surface ll and a securing bracket i5, is mounted by means of the bolt I6 on the connecting bar I l. The stationary contact II may be engaged by the movable contact I! which also is an L-shaped member having a contacting surface it and a mounting bracket It. A bolt passes through the mounting bracket I9 and secures the movable contact ii to the upper portion of the movable contact carrying lever 22.

Lever 22 is pivoted for rotational movement at 23. A flexible laminated conductor 24 is secured in any suitable manner, as for instance, by the bolt 25 to the lower end of the lever 22, and at its opposite end is secured by the bolt 28 to the end of the connecting bar l2.

when, therefore, the circuit breaker contacts are closed, a circuit is completed from conductor il through the stationary contact I; to the 'movable contact I] through the movable contact carrying lever 22 and the flexible lead 24 to the connecting bar ii. A tension spring 30 is connected at one end to the ear ii on the movable contact carrying lever 22, and at the other end, the spring Iii is connected to a lug 32 mounted on the frame of the mechanism. Tension spring 30 therefore biases the movable contact carrying lever 22 into counterclockwise rotation and hence biases this member to open circuit position.

When the circuit breaker is open as seen in Figures 2 and 3, then the movable contact lever 22 rotates counterclockwise against the stop 34, which limits further rotational movement thereof. The said stop is, of course, arranged in such position as to permit the movable contact to move a suflicient distance away from the stationary contact to ensure proper circuit interrupting capacity.

When closed, the contacts are normally maintained in engagement by means of the flexible member 35, which may take any desired form, such as a chain. The chain I5 is connected at one end to an car 28 mounted on the contact .lever 22 preferably approximately midway between the pivot point 23 and the free end which carries the movable contact II. This chain passes over the roller 31 which is mounted on the operating crank 38. The other end of the chain is at 19 secured to the armature III which is normally held in engagement with the operating magnet 42.

The armature 40 is pivotally mounted on the lever 44 which is rotatably mounted on the pivot 45, which in turn is carried by lugs 48 associated with the frame of the mag et 42.

' The magnet 42 is normally energized b a con-' stant potential direct current coil 41 which prohereinafter described to close or to open the circuit breaker independently of the magnet 42 and the armature 40.

A motor 50 is used to operate a multi-pole unit. driving, through an insulating shaft, the high speed shaft 5| of small speed reducers 52; one speed reducer being mounted on each pole. The low speed shaft 53 of each speed reducer carries the crank 38 and its roller 31.

If the motor 50 is run sufliciently to drive crank 38 through 360 and the armature 40 is sealed against the pole face of magnet 42. the effects of the chain riding on the crank roller 81 is to cause the breaker to go through an open-close cycle, as shown in Figures 1 and 3.

A limit switch may be utilized for controllin the motor which, with suitable braking, ensures that the crank and roller will stop at the proper point in the operating cycle either for closing or p ing.

In Figure 2, the circuit breaker contacts are shown in the open position, having opened automatically because the flux in the magnetic path of magnet 42 and the armature III was reduced beyond the critical value necessary to counter- 281181108 the tripping force exerted by the spring Accordingly, the spring I0 has caused the lever 22 to rotate counterclockwise, thus pulling the chain 35 over the roller I1 and lifting the armature 40 away from its magnet 42.

Figure 3 shows the flrst necessary step for reclosing the circuit breaker after it has operated open to the position shown in Figur 2. with the breaker contacts disengaged and armature I in its uppermost position, the crank 38 is rotated by motor I0 through 180 so that the armature is permitted to fall by gravity against the pole face of magnet l2, and the flexible member I! is shown completely slackened having no tension at this particular phase of the operation. The circuit breaker may now be reclosed by energizing the coil 41 to assure that there is adequate holding flux passing through the armature ll. The shaft 51 is then rotated by means of the motor preferably in a clockwise direction to rotate the crank 38 and the roller 21 so that flexible member 35 is drawn taut and then is efvides adequate flux to maintain the armature lll in contact with the pole pieces against the pull of the spring Ill transmitted by the chain or flexible member 38.

Current flowing through the series conductor l2 affects the flux between the magnet and the armature so that under certain conditions of direction and intensity of current flow, as hereinafter described, the flux through the armature is inadequate to counteract the effect of the spring 20, and the circuit breaker contact is pulled to open position.

The crank 32 may be operated for the purposes fective to pull the contacts into engagement and maintain them in the position shown in Figure 1.

To open the circuit breaker without relying on the automatic circuit breaker opening means, the field coil 41 may be deenergized, which will result in the release of armature l0 and a consequent opening of the circuit breaker; or the motor I may be rotated so that shaft 53 is rotated through thus bringing the circuit breaker to the position shown in Figure 3. In each case, the circuit breaker may be opened.

In the foregoing, the principle of the formation of my circuit breaker has been set forth in its simplest form. I

Either of the contacts I! or II may obviously be resiliently mounted upon their respective supports.

The type of holding magnet shown in Figures 1, 2 and 3, is of a conventional bucking bar" type well known in the art. The actuating mechanism of the circuit breaker may, of course, be effective with any of the'well-known releasable holding means. The type of holding magnet which I prefer, however, to use in the circuit breaker of the present type, and which also has many additional functions and operations, is that shown in Figures 5 to '7 inclusive.

During normal operation of the circuit breaker when the circuit breaker is closed, as seen in Figure In, current passes from the upper connected terminal III in the direction indicated by the arrows through the blow-out coil 350 of the arc chute 351 to the stationary contact structure Stationary contact structure 3l3 is engaged by the movable contact 3 which is mounted on the upper portion of the movable contact lever 322. Lever'322 is pivoted at 323 on the frame 318 of the circuit breaker.

A pigtail connection 324 is provided between the contact 311 and the conductive frame 318.

Current then flows to the front terminal assembly indicated generally at 31I, whence it flows through the bucking bar 3l2a to the lower connecting terminal 3I2.

The blow-out coil 388 in the arc chute 36| may be of the formshown in Patent No. 2,405,454, issuedAugust 6, 1946, to William M. Scott, Jr., or in Patent No. 2,381,637, dated July 31, 1945, to Donald I. Bohn, each of which is assigned to the assignee of the present application.

When the contacts 313 and 3|1 are closed, the circuit is then completed from the connector 3 through to the connector 3I2.

A tension spring 330 is connected at one end to the link 33l which, in turn, is connected to the movable contact lever 322-and at the other end,

the said spring 333 is connected by means of the adjustable nut 332 to the frame of the mechanism. Tension spring 338, therefore, biases movable contact carrying lever 322 into counterclockwise rotation and thus biases this member to open circuit position.

The member 334 carried by the link 33l acts as a stop against the stationary cover plate 334a of the housing for the spring 330 when the circuit breaker is open, as seen in Figure 2athus limiting further rotational movement of the lever 322 in counterclockwise direction.

The stop members 334 and 334a are, of course, arranged in such positions as to permit movable contact 3| 1 to move a sufficient distance away from the stationary contacts to ensure proper interrupting capacity. I

When the contacts are closed, as shown in Figure in, they are maintained in engagement by means of the chain 335 which is connected at one end to the pin 33la of link 33! (and is, therefore, connected to the movable contact lever 322), and which is secured at its opposite end to the armature 348 which is normally held in engagement with the magnet 342.

Armature 340 is rigidly mounted on the lever 344 which is rotatably mounted on the pivot 345 which, in turn, is carried by the extension 346 associated with the frame of the magnet 342.

The magnet 342 is normally energized by' a constant potential direct current coil 341 which provides through the pole pieces 341a adequate flux to maintain the armature 340 in contact with the pole pieces of the magnet 342 '(in the manner hereinafter described) against the bias of the spring 330 transmitted through the chain 33 The chain 335 passes over the roller 33'! which is mounted on the operating gear 338.

Current flowing through the bucking bar 3l2a affects the flux between the magnet and the armature (as hereinafter described), so that under certain conditions of direction and intensity of flow, the flux through the armature is inadequate to counteract the effect of the spring 330, and the movable contact 3l1 is pulled to open position. This open position is shown in Figure 2a, where it will be seen that the stop members 334 and 334a of the contact lever have been engaged as the contacts open. It will also be seen that a suitable shock-absorbing stop 340a is provided for the armature 340.

Thegear 338' may be operated to close or to open the circuit breaker independently of the magnet 342 and the armature 340.

A motor 350 is used to operate a multi-pole unit driving each of the units simultaneously. Motor 350 is connected by the belt 380 and pulley "I to shaft 382 which is preferably an insulating shaft extending through the entire multi-pole unit to drive all of the elements simultaneously.

Pinion 383 on shaft 332 drives the gear wheel 338.

If the motor 358 is run sufliciently to drive the gear 338 through 360 and the armature 348 is held against the poles of the magnet 342, the effect of the chain 335 riding on the roller 331 is to cause the circuit breaker to go through an open-closed cycle as shown schematically in Figures 1 to 3.

In Figure 2a,- the circuit breaker contacts are shown in the open position, having opened automatically because the flux in the magnetic path of magnet 342 and armature 348 was reduced beyond the critical value necessary to counterbalance the tripping force exerted by the spring 338. Thus, the spring 330 is causing the lever 322 to rotate counterclockwise, thus pulling the chain 335 over the roller 331 and lifting the armature 340 away from its magnet 342. By now rotating the roller 331 through 180", the chain 335 that the coil spring 385 engaging the armature arm 344 will be free to drive the armature 34. toward the pole face of magnet 342.

Coilspring 385 is suiiiciently light so that it will not interfere with the opening of the circuit breaker. Yet, when the chain 335 becomes slack by reason of this 180 rotation of the gear 338, the coil spring 385 will have sufllcient force simply to re-set the armature 340.

Since current no longer flows through the bucking bar 3|2a by reason of the opening in the circuit breaker, the coil 341 will generate sufficient flux in the magnet 342 to hold the armature 340 and the magnet 342 together despite the tension on spring 330.

Now, therefore, when the gear 338 is rotated through another 180, the roller 331 and all of the other elements of the circuit breaker will be brought back to the position shown in Figure 1a.

This is so since one end of the chain 335 is effectively anchored by the holding of the armature 340 against the poles of magnet 342 and the other end is secured to the contact lever.

Thus, the circuit breaker may be opened in two ways: one, by rotating the gear 338 through 180 to slacken the chain 335; the other, by de-energizing magnet 341 which will reduce the flux sufficiently to cause a release of the armature 340.

The circuit breaker will, of course, be tripped of Figure 2a will be slackened so in accordance with the Principles herelnbefore and hereinafter pointed out, where, in a reverse current flow, as indicated in Figure 2a, the flux generated by the current flowing in the bucking bar 312a will oppose the flux generated by the coil 34'! and thus reduce the net flux through the magnet 342 and armature 340 sufficiently to permit the spring 330 to effect a separation of the magnet and armature.

The manner of the mounting of the circuit breaker here shown has not been described in detail since it corresponds exactly to the manner of mounting of the circuit breakers shown in Patent No. 2,393,687, dated January 29, 1946, to Otto Jensen and in Patent No. 2,405,454, dated August 6, 1946, to William M. Scott, Jr., which are assigned to the assignee of the present application. It is sufficient to say that a clamping plate 300 and clamping bars 39I secure the entire mechanism to parallel insulated cross bars 392 which are in turn secured by clamping plates 393 and bolts 394 to opposite longitudinal channels 305.

In the device here shown a simple indicating means is provided to show the condition of the circuit breaker. A lever 396 is pivotally mounted at 391 on the frame 310. One end of the lever is pivotally connected at 33Ia to the link 33I. The other end of the lever bears against the indicating rod 301 which is biased inwardly by the compression spring 390.

When the circuit breaker is in the closed circuit position shown in Figure 1a, the lower end of the lever 396 bears against the rod 361 to force it outwardly to the dotted line position against spring 398 to indicate the closed circuit position.

When the circuit breaker is opened, the lever 396 rotates counterclockwise thus permitting the spring 390 to force the rod 301 to the right and draw the rod inwardly thereby indicating the open circuit condition.

It is obvious, of course, that the stationary contact structure 3I3 is insulated from the remainder of the circuit breaker as shown, since the remainder of the circuit breaker structure, including the main frame or housing 310, is conductively connected to the movable contact member 3I'I.

Referring now to Figure 4, there is here shown in partially exploded form the holding magnet which constitutes a primary element of my invention. The holding magnet, as may be seen in Figure 4, comprises a rectangular structure consisting of stacks of laminations which provide spaced and interleaved pole pieces of opposite polarity. This system provides a plurality of '1 short flux paths (hereinafter described in connection with Figure through the armature and results in an extremely quick acting release. The electrical and magnetic properties and the advantages in actual operation of my holding magnet will be more specifically set forth after the following description of the specific physical arrangement thereof.

The stacks of laminations are held together by a pair of non-magnetic frame plates IOI and I02. Plate ml is provided with a plurality of tapped perforations I03, I03 to receive the ends I04, I04 of a plurality of studs I05. Studs I05 are insulated from the metallic laminations hereinafter set forth by the insulatin bushings I06, I06. These studs I05 pass through corresponding openings I00, I00 in each of the metallic laminations as hereinafter set forth, and also pass through openings in the lower plate I02-all of the openings in the plates and in the lamina- 8 tions being in registry with each other. The lower end of the studs are also threaded, and the entire assembly is securely integrated as a single unit by means of the nuts I I I which are threaded onto the ends IIO of the studs I00, and held in place by the lock washers II Ia and washers lb. The washer IIIb is of insulating material to ensure that the nuts III are appropriately insulated from the plate I02.

A central opening H5 is provided in each of the plates WI and I02 and registers with corresponding openings in each of the laminations formed by the plurality of magnetic sheets. as hereinafter set forth, in order to form a central opening through the entire structure through which the conducting bar I2 passes.

In Figure 4, the plate 101 and one layer of laminations and its associated insulating spacing plate is shown lifted from the entire stack in order better to illustrate the complete unit.

In the construction shown in Figure 4, the holding magnet is provided with flve layers of laminations I2I to I25. Each of these layers of laminations is separated from the adjacent layer by insulating plates I26 to I29 respectively.

Referring now to layer I2I, this layer, as do each of the others, consists of two sets of laminations. One of the sets or stacks I32 comprises sheets which are L-shaped in formation with one limb I33 forming the sides of the structure and provided with openings I00, I00 to receive the studs I00. The other limb I00 forms a magnetic pole in the manner hereinafter described.

Layer I2I comprises, in the same plane with laminations I32, another stack or layer of laminations I40 which consists of a plurality of sheets of a simple rectangular form and which forms an element of the other side of the structure. The stack I40 is also provided with openings I00, I00 to receive the insulated bolts. An air gap I42 is provided between the limbs III forming a pole piece, and the end of the rectangular stack of laminations I40. The insulating plate I26 is placed immediately beneath the layer I2I and immediately above the layer I22 in surface to surface engagement on opposite sides with each of the layers.

While sheet I26 should preferably be an insulating non-metallic sheet, it is suflicient. however, for purposes of operation of the holding magnet that it merely be a non-magnetic member. The insulating sheet I20 is U-shaped in formation and is provided with the central opening II5a which registers substantially with the central opening H5 in each of the outer plates I02 and IN to permit the conducting bar I: to pass therethrough. Sheet I20 also has openings I00, I00 to permit the insulating bushings to pass therethrough.

The next group of laminations immediately beneath, that is, layer I22 has the same form as the laminations in layer I2I, but the members are reversed with respect to each other. Thus, the stack M in layer I22 extends immediately beneath the limb I33 of stack I32 in layer I2I; and limb I030, of stacks I32a in layer I22 extends immediately beneath the stack I40 in layer I2I.

In layer I23, the positions of the stacks are agalnreversed so that the L-shaped stack extends beneath the L-shaped stack of layer I2I. and the rectangular stack of layer I20 extends beneath the rectangular stack in layer I2I.

In layer I24, the positions are again reversed 9 so that the arrangement of the stack corresponds exactly to that of. layer I22; and again in layer I25, the positions-are reversed so that the arrangementof the stacks inthe layer corresponds to the arrangement in stacks I23 and I2I,

Thus, in each adjacent layer, an L-shaped stack is in alignment with a. rectangular stack, and a rectangular stack on the opposite side is correspondingly in alignment with the adjacent L- shaped stack on either side of the layer.

Insulating-spacing plates I21, I28 and I28, similar in every respect to spacing plate I25,

' are introduced between successive layers of laminated stacks so that each successive laminated layer I 2I-I25 is magnetically isolated from the others.

The laminated stacks, as well understood, are formed of magnetic material so that appropriate magnetic fluxes may be created in accordance with the operating characteristics hereinafter set forth.

An air gap I42 is provided in each layer between the rectangular stacks and the adjacent limb I35 of the L-shaped'stack in the same layer-for purposes hereinafter described in connection with Figure 14.

The pole pieces are formed by the limbs I 35, I35a, I35b, I350 and I35d in the stack. Adjacent poles in adjacent layers are of opposite polarity in accordance with the structures hereinafter described. Thus, should pole I35 be north, then pole I35a will be south, I35b north, I35c south, and I35d north. The poles of opposite polarity are interleaved as shown in Figure 4 so that they extend substantially between each other to .provide proper terminals for the magnetic paths through the armature in the manner hereinafter described. The manner in which the poles become of opposite polarity should be obvious upon inspection of Figure 4. Thus pole face I 35 extends from the right-hand end I32 of the structure, and current induced in the laminated stack will produce a magnetic flux of a specific direction therein.

In layer I22, the fluxes will be of the same direction, but, however, pole face I35a extends from the left-hand side of the stack, and hence this pole will be of a polarity opposite to that of pole I35. Similarly, pole l35b extends once more from the right-hand end of the stack and pole I350 from the left-hand end so that in each case the polarity will be opposite. The arrangement is fol-lowed throughout the stack so that adjacent interleaved poles are of opposite polarity.

,In order to complete the magnetic circuit between the ends of the laminations remote from the pole pieces, a single stack of rectangular laminations I50 is provided. This stack of laminations is secured between the end frame members IM and I02 in spaced relation to the ends of the other laminations so that an air gap I5I is provided between the ends of stacks I32 and I40 and the stacks I50. This is done in order to reduce the possibility of saturating the magnetic material during normal operation.

The stack I50 is maintained in position, as will be obvious in Figure 4, by the insulated studs I05 which pass through corresponding registering openings in the stacks and in the end frame members.

This flux in the schematic showing of Figure 5 will flow through pole I6l through one of the magnetic laminations I35 and then through the armature 40 to the adjacent opposite pole I 35a,

' l0 returing through pole piece I. A parallel magnetic circuit is provided from pole piece III through laminations I351), armature II to laminations I35a, returning through pole piece I00. The flux flowing in laminations I35b divides as shown in Figure 5, some flowing through the armature 40 to laminations I350 and pole piece The manner in which the flux flows from pole to pole through the armature in each case is shown in the schematic cross-sectional view of Figure 5.

Thus, the flux in the laminations is divided into a plurality of parallel flux paths through the armature, each of the paths including only its individual portion of the armature as distinguished from prior magnet structures in which all of the flux in the magnetic Structure must flow through the entire armature. Accordingly, for the same armature mass, my present structure will conduct a considerably larger number of flux lines by reason of the number of multiple magnetic paths than is the case of the standard magnet in which all the fiux flows through the entire structure in a single series path.

In Figure 5, I have shown a cross-section through the magnetic pole pieces and the armature along approximately the center line. Again, since the armature need only be of Sn!- ficient thickness and strength to carry the flux between adjacent pole pieces, and thus is, in effect, a plurality of small armatures bridging separate air gaps, the cross section of the armature may become so small in respect to the physical force existing that in an armature of uniform cross section, an effect may very well be created wherein the center of the armature may be deflected. That is, the point 39, at which the eX- ternal force exerted by the flexible chain 35 is exerted, may be drawn away from the pole face owing to the relatively small cross section required for the armature. In such a case, the slight flexing of the armature, which permits the center area thereof to be drawn away, may thus decrease the magnetic flux therethrough at the center. This decrease in magnetic flux at the center will thus decrease the net counteracting force exerted by the magnetic structure to the pull at the point 39, thus permitting the pull to be exerted more strongly, thus making it possible for the center of the armature to be deflected even more, and thereby permitting a greater portion of the armature to be drawn away. This successive action, which may occur very quickly, will, owing to the flexing of the armature, permit the armature to be released.

Accordingly, the armature 40 is thickened at 60 its center portion to provide a better path for the passage of magnetic fluxes thereat, and the center stack of laminations is thickened so that the center pole face I352; is much thicker than the other pole faces.

Similarly, the pole faces adjacent the center pole face, that is, pole faces I35a and I350, while not as thick as pole face I 35b, are much thicker than pole faces I35 and I35d.

Since the stacks of laminations toward the 7 center of the magnetic structure have the greatest thickness, consequently, they also have the greatest pole area and provide the largest amount of flux flowing into the armature. The armature itself, since it is thickened at the cen- (5 ter, also provides an appropriate path for this increased amount of flux. This flux is progressively decreased toward the center of the armature.

It thus becomes possible to provide an armature of a minimum weight with greater physical strength than in cases where an armature structure of uniform cross-section throughout is used.

Thus, in Figure 5, the poles I35, I35b and I35d are indicated as being north. Flux lines 200 flow from pole I35 into the intermediate pole I35a. Also, flux lines I flow from pole Id into the intermediate pole I35c. Flux lines 202 and 203 flow from the central pole I35b into the intermediate poles I35a and I350. In each case, the magnetic circuit is completed from pole to pole through the pole pieces I60 and I6I through the core I01.

On the occurrence of reverse current conditions in the bus bar I2, the flux tending to hold armature in place against the force of the counteracting spring is reduced so that the armature is permitted to move away from the magnetic structure. As armature 40 moves a slight distance away from the magnetic structure, as shown in Figure 6, thus creating the air gap 2I0, then, under normal or steady current conditions, the introduction of such an air gap will cause the building up of the leakage between the adjacent poles so that the flux passing into the armature is so rapidly reduced that the pull exerted by the magnetic structure becomes substantially zero at a very small air gap 2 I0, and the armature may then be drawn away from the magnetic structure very quickly.

During practical operating conditions in some installations, a fault current may increase in value at an exceedingly high rate. There are installations in which the rate of rise in current may be increased at ten million amperes per second. Under such conditions, it is essential that the speed of movement of the armature and the rate of rise of the flux in the air gap be so arranged that there shall be no tendency for the armature to be drawn back against the pole piece and so prevent the opening of the circuit breaker.

While the condition shown in Figure 6 represents a leakage flux from one pole piece to an adjacent one, which will occur during normal operating conditions, high rate of rise may change this action. At a very high rate of current rise,

the flux increases correspondingly. I have found that rapidly changing flux will flow normally parallel to the plane of the laminations, and that they are so guided by the outer laminations that the cross leakage is substantially zero. Any flow of this flux of rapidly changing value normal to the plane of the laminations would tend to create eddy currents which would tend to oppose the cross flow. As a result of this condition, the situation shown in Figure 13 would not exist during a fault involving a very high rate of rise in current, and for this reason, it is necessary to provide, as shown in Figure '7, a relatively narrow air gap between the ends of a pole I35 and the rectangular stack I40. This air gap will provide a leakage for the flux produced by a current changing any value of rate of rise so that the tendency to draw the armature back against the pole pieces is eliminated.-

From the above, it will now be clear that the magnetic path for fluxes flowing through the pole piece I is distributed through the laminations I2I to I25. Because of the variation in the number of laminations in section I2I as compared to the next section I22 and I23. less lines of force will flow in the laminations I2l. a greater amount of flow in I22 and still a greater amount in I22. The lines of force flowing in laminations I35 of layer I2I will in turn divide themselves, a larger proportion of such fluxes flowing from the lamination I35 to lamination "5a through the portion of the armature bridging I35 and I35a as shown at 200 in Figure 5.

A smaller proportion of such fluxes flows from lamination I35 through the armature which bridges the gap I42 to the layer I40. This is due to the fact that the reluctance of the smaller path to the armature from layer I35 to I00 is greater than the reluctance of the much larger path provided by the armature from layer I25 to I354.

Moreover, the lines of force flowing in the magnetic structure are greater than the lines of force which could be carried by the armature cross-section at this point which further determines the distribution of lines of force.

In general, the distribution of magnetic lines of force is as illustrated in Figure 5. A relatively small number of lines flows from lamination I05 to I35u through the armature of reduced crosssection. A much larger number of lines 202 flows through laminations I35a and "5b through the armature of greater cross-section at this point. Thus, the portion of the armature which is subjected to greatest load also has the greatest mass of material and carries the largest number of lines of force and the portion of the armature which carries the least load is of the least cross-section and carries the minimum number of lines of force.

This is better shown and more evident from an examination of Figure 5, which shows portions of the metal between the lines of force 202 and 203 which perform no useful function in carrying magnetic lines of force.

This same principle may be carried out in other portions of the armature, if desired.

With the previous breaker, the current reached a value under a certain set of test conditions of 30,000 or 35,000 amperes when arcing was initiated; whereas, with this higher speed breaker, arcing may be initiated at appreciably less than half this value. As a consequence, satisfactory speed of arc travel during the early formation of the arc with the prior arc extinguisher was unsatisfactory, resulting in distress and delayed current limitation.

While I have here described my invention in connection with preferred, successful embodiment thereof, many variations in the actual form of the interleaved pole pieces, and many variations in the form and construction of the armature and of the circuit breaker itself, as well as many variations in the bucking bar" arrangement and in the exciting coil and other elements of my invention, will now be obvious to those skilled in the art. Accordingly, I prefer to be bound not by the specific disclosures herein, but only by the appended claims.

I claim:

1. In a circuit breaker for protecting an electric circuit having a flxed and a movable contact having a spring for normally biasing said movable contact to disengage said flxed contact, an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection from said movable contact to said armature, a source of power interposed between said movable contact and said armature of said electromagnct for operating said movable contact while sai".

electromagnet is energized against the biasing action of said spring to efl'ect engagement of said contacts and for maintaining said flexible connection taut, said source of power being operable to loosen said connection from said movable contact to said armature whereby said armature may be operated by said electromagnet to engaged position with the pole face thereof without operatingsaid movable contact.

2. In a circuit breaker having a fixed and a movable contact, an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection from said movable contact to said armature, means including a source of power interposed between said movable contact'and said armature of said electromagnet for maintaining said flexible connection taut, said means being operable to loosen said connection from said movable contact to said armature, said armature being operable by said electromagnet, while said connection is loose, to engaged position with the pole face thereof without operating said movable contact, said power means being operable to bring said flexible member to a taut position for operating said movable con tact to engaged position with the fixed contact after said armature is in operated position against its pole face.

3. In a circuit breaker having a fixed and a movable contact biased to disengaged position, an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible con nection from said movable contact to said armature, means including a source of power interposedbetween said movable contact and said armature of said electromagnet for maintaining said flexible connection taut, said armature on de-energization of said electromagnet being operated by said biased contact away from said electromagnet, said means being operable to loosen said connection from said movable contact to said armature whereby said armature may be operated by said electromagnet to engaged position with the pole face thereof without operating said movable contact, said electromagnet on de-energization operating to permit said movable contact to disengage its fixed contact while maintaining said flexible connection taut.

4. In a circuit breaker having a fixed and a movable contact, said movable contact being normally biased to disengaged condition, an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection from said armature to said movable contact, means including a source of power interposed between said armature and said movable contact for maintaining said flexible connection taut, said movable contact being selectively responsive to said interposed means and said armature for operating said movable contact to disengaged position by the operation of said interposed means to a position at which said flexible connection is loose while said armature is maintained in energized condition and in response to de-energization operation of said armature while said interposed member maintains the taut con dition of said flexible connection.

5. In a circuit breaker having a fiixed and movable contact biased to disengaged position, an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection from said movable contact to said armature, means interposed between said movable contact and said armature of said electromagnet for maintaining said flexible connection taut, said means being operable to loosen said connection from said movable contact to said armature to effect disengagement of said contacts, said armature being operable by said electromagnet to engaged position with the pole face thereof without operating said movable contact to engaged position and means for operating said interposed member to bring-said flexible member to a taut position for operating said biased movable contact to engaged position with the fixed contact while said armature is in operated position against its pole face, said armature having a maximum cross-section at the center and a minimum cross-section at the ends, said flexible connection being connected to said armature at its center and at the point of maximum crosssectional area thereof.

6. In a latch free circuit breaker having a movable contact element having a closed and an open position for controlling an electric circuit; an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected; a flexible connection from said armature to said movable contact element for maintaining said contact in its closed position when said magnet is energized; means connected to said contact element for moving it to its open position directly in response to the de-energization of said electromagnet in response to a change in the electric circuit conditions; means operating on said connection for freeing said armature from said contact element to permit said electromagnet to be re-energized to operate the armature to its original position while said contact element remains in its open position, and means interposed between said contact and said operating means for operating said contact element to its closed position and for restoring said armature control over said contact element in its closed position.

'7. In a circuit breaker having a movable con tact element having a closed and an open position; means for biasing said element to open position; an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection from said contact element to the armature of said electromagnet for maintaining said contact in its closed position when said electromagnet is energized; said flexible connection being operated by said biased element on the de-energization of said electromagnet in response to circuit conditions for permitting operation of said contact element to its open position; means interposed between said contact element and armature, said means and said electromagnet being jointly operative to restore said contact element to its closed position against the action of said first mentioned means, said electromagnet remaining energized to maintain said contact element in its closed position.

8. In a circuit breaker having a movable contact element having a first and a second position; an electromagnet having an armature and connected to be responsive to current conditions in the electric circuit being protected, a flexible connection" from said armature to said movable contact for maintaining said contact in its first position when said electromagnet is energized; means operative on the de-energization of said electromagnet in response to circuit conditions 15 for operating said contact element to its second position; means interposed between said first means and said armature, said second means and said eiectromagnet jointly operating said contact element to its first position against the 5 action of said first mentioned means; said electromagnet remaining energized for maintaining said contact element in its first position.

DONALD I. BOHN.

REFERENCES CITED The following references are of record in the file of this patent:

Number Thumim Mar. 22, 1938 

